The present invention relates to a circuit arrangement for judging the lifetime of a battery in a no-break power supply system.
In a conventional no-break power supply system, as shown in FIG. 1, the AC power of an AC power supply source P (commercial power source) is converted into a DC power through a rectifier Rec and a smoothing capacitor C and the DC power thus obtained is again inverted by an inverter IV, including an automatic voltage regulating means, into an AC power having a constant voltage and constant frequency, which is supplied to a load L such as a computer or the like so that the load L is operated with such an AC power under a normal condition of the AC power source.
While, under such a condition, the AC power source P charges, through a charging unit CH under a floating charge condition, a battery B having one electrode connected to the ground and the other electrode connected to the input of the inverter IV through a diode D, so that the battery B compensates for the supplying power to the inverter IV when a service interruption occurs or the output voltage of the rectifier Rec becomes lowered by some failure. This floating charge system is suitable for the no-break power supply system comprising the battery with comparatively small capacity.
In another conventional no-break power supply system, as shown in FIG. 2, the AC power of an AC power supply source P (such as a commercial power source) is converted into a DC power through a rectifier Rec such as a thyristor and a smoothing capacitor C and the DC power thus obtained is again inverted by a inverter IV including an automatic voltage regulating means, into an AC power having a constant voltage and constant frequency, which is supplied to a load L such as a computer of the like. In this case, the rectifier Rec has to charge, under a floating charge condition, a battery B connected between the input of the inverter IV and a ground in order to compensate for the DC power in the case of service interuption, so that the conducting phase of the rectifier Rec is controlled by a thyristor control circuit CN1 so as to adjust the DC power finely. This floating charge system is suitable for the no-break power supply system comprising a battery with comparatively large capacity.
In comparatively large scale no-break power supply system using a stationary battery, even in the circuit arrangments shown in FIGS. 1 and 2, an ordinary maintenance may judge the lifetime of respective batteries with easy by regularly checking the voltage, the specific gravity or the like of the respective batteries. In recent small no-break power supply systems with easy maintenance and small capacity, small enclosed lead storage batteries are actively used. When such an enclosed type battery is used, it is difficult to judge the performance or lifetime of the battery because of the enclosed structure. Particularly, as the lifetime of the battery approaches the end thereof, it is necessary to try a discharging test to decide the term of exchanging the battery. Even if the battery is not approaching the end of its lifetime, when one of cells or batteries fails since the number of series connected cells is usually several tens, the discharging property deteriorates and, in the extreme case, the no-break power supply system does not actuate, so that the voltage across the load decreases rapidly with service interruption of the commercial power supply source resulting in an infection onthe load being the computer. In order to avoid such a condition, the battery must be actually discharged to check such a condition.
In the conventional system shown in FIGS. 1 and 2 generally, the service interrupting condition is forcedly generated during operation of the no-break power supply system to discharge the battery thereby performing such a check. If at such a checking, failure of the battery has been generated, the output voltage of the no-break power supply system is abnormally decreased, thereby causing an infection on the load such as a computer down. Actually, the discharging test of the battery is difficult under the forced service interrupting condition during operation of the no-break power supply system.